1. Field of the Invention
This invention relates to and is useful for selectively controlling the angle of a well hole or a borehole as it is cut through earth material or the like. More particularly, the present invention relates to controlling the advancement angle of a borehole by selectively removing a different amount of material over a selected partial arc of a gage corner formed by a rotary drill bit.
2. Brief Introduction and Description of Prior Art
A variety of different methods and arrangements to control the advancement angle of a borehole are known and conventionally employed. Although the majority of these approaches are successful and reliable, certain disadvantages are inherent. Usually, changing or controlling the borehole deviation or advancement angle requires use of special drill bits, support collars, and special methods of drilling. In each case, the conventional drill bit and drill string must be pulled from the borehole and the special equipment inserted. After achieving the desired angle change, the special equipment is removed and use of the conventional equipment is resumed. Of course, each time an angle change is made, there is an obvious loss of drilling penetration rate while the special equipment is inserted, used and then removed. Control and guidance equipment is typically required for conventional angle change apparatus and methods and this equipment is generally very expensive and may require the presence of specially trained personnel to operate and control the equipment. Since a major factor in drilling well holes is time consumed, it is important to maintain a good drilling or penetration rate and to minimize the time when actual drilling does not proceed. Reducing the costs involved in making angle changes with conventional equipment is a further important factor in reducing the total cost of drilling boreholes.
Other disadvantages and limitations are known and appreciated by those knowledgeable in the art. Many of these prior art disadvantages and limitations can be overcome or significantly minimized by the present invention.